Tomato-based products such as tomato ketchups, barbecue sauces, pizza sauces and other similar condiments are typically made from tomato pastes, tomato purees, tomato juices or similar compositions that contain substantial amounts of tomato solids. These tomato solids include water-insoluble tomato particles, including tomato seeds and portions of tomato skins; tomato fibres which comprise the bulk of tomato fruit; and pectin. Each of these components affects the stability, appearance, flavour and sensory appeal of tomato-based food products.
For example, the carotene lycopene that gives tomato sauce its characteristic red colour is found primarily in chromoplasts within the tomato pulp and tomato fibre. Hence, the amount and distribution of the pulp and fibre will determine whether the tomato sauce will have an overall, even desirable colour. In addition, the size and distribution of the tomato pulp particles may also affect the texture of such tomato-based products. Large, unevenly distributed pulp particles will tend to produce a lumpy product, while extremely finely divided pulp particles will tend to produce a smooth textured product.
Similarly, the tomato fibres tend to link together and intertwine to form a lattice network or fibrous matrix that provides body and viscosity to tomato-based products and further traps free liquid which would otherwise “weep”, i.e. separate, from the product. The liquid typically consists primarily of water and may also include other tomato fluids, and additives to the product. When present in sufficient concentrations, the pectin in tomato-based products forms a gel that also acts to bind free liquid in the products and to increase the products' viscosity.
http://all-creatures.org/recipes/i-tomatopaste.html discloses a standard canned tomato paste prepared by cooking tomatoes until a concentrate with 73.5 wt % water content is obtained, containing (calculated on dry weight) 16.3 wt. % protein, 37.4 wt. % glucose and fructose taken together, 0.11 wt % lycopene and 17 wt. % dietary fiber.
It is known to modify the physical properties of the tomato solids in tomato sauces and slurries using various techniques, including homogenisation of the products. Homogenisation is employed to finely divide, break down and disperse pulp particles throughout a slurry to produce products with acceptable colour and texture. Tomato pulp contributes many relatively spherical particles, which are insoluble in water and which must be reduced in size and uniformly dispersed throughout the product. If this is not done, a product with an excessively rough texture will result. Furthermore, since the carotene pigment (lycopene) is contained in these particles of pulp and fibre, failure to properly disperse them will result in a product with poor uniformity and depth of colour.
In addition to the above particles, tomato dispersions have a very high content of fibrous strands. Through proper processing techniques, these fibres form a structure that is responsible for the viscosity of the product and for its ability to retain free water. Homogenisation can cause fibrillation of the fibre ends without a significant reduction in fibre length. This results in fibres having ends similar in appearance to the ends of a frayed rope. The fibrillated fibre will absorb and retain water in the manner of a wick. The obvious result is increased product viscosity and reduced syneresis.
However, the process does have limitations. If too high a homogenizing pressure is used, then the fibre network will be broken down. Although the greater number of individual fibres will absorb more water and cause a greater viscosity increase, any remaining free water will quickly separate because the structure which bound this water will have been destroyed. In short, the price for greater viscosity increases is an increase in serum separation. In practice, processing conditions are chosen on the basis of a compromise between these two opposing effects.
A component that plays an important role in the preparation of tomato dispersions is pectin. This naturally occurring polysaccharide increases product viscosity and reduces separation by tying up any remaining free water. Homogenization increases both of these effects by aiding in the complete and uniform solubilisation of the pectin.
Obviously, the preparation of tomato products is very much subject to variations in the structure and chemistry of the tomatoes used. This, in turn, is dependent upon such growing factors as: geographical location, climate conditions, weather variations, soil conditions, growing season and variety of tomato. There is no way to eliminate the influence of such factors. However, adjustments in homogenising conditions may be required to compensate for unwanted characteristics in the final product resulting from these factors. This type of precise control over the physical characteristics of the finished product is very important in maintaining a degree of consistency from batch to batch.
Alternative processing steps have been used to supplement the effects of homogenisation, including the additional steps of milling the products or using of vacuum expansion chambers to increase viscosity and improve the colour of the products.
Despite the efforts that have been made to optimise the stability, appearance, flavour and sensory appeal of tomato-based food products by manipulating the processing conditions that are employed in the manufacture of these products, it is common practice to employ additives, notably calcium chloride and/or viscosifiers, to further improve stability and texture of tomato-based products. In the tomato processing industry calcium chloride is frequently added to tomato products to increase their viscosity and to prevent syneresis. The calcium ions react with free carboxyl groups of tomato pectin to produce a gel network of calcium pectate. Viscosifiers such a natural gums, starch, pectin, guar gum, xanthan gum and CMC are also widely used to increase the viscosity of and/or to prevent syneresis in tomato-based products such as ketchup. From a consumer perspective, the use of such additives in tomato products, notably the use of additives that are foreign to tomatoes, is undesirable.
Farahnakyi et al., Journal of Texture Studies, vol. 39. (2007), pp. 169-182 describe a method for preparing a thickening agent, involving drying tomato waste (“pomace”, mainly including tomato seeds and skins) to a moisture content of about 7%, followed by milling and sieving. This results in a tomato pomace powder comprising (on dry matter) 24.8 wt % protein, 0.08 wt % lycopene, 13.8/14.5 wt % reducing sugars/total sugars and 41.1 wt % fibers.
U.S. Pat. No. 6,413,560 describes a method for preparing a pectin-containing food, said method comprising treating a food mass with pectin esterase under conditions which result in (i) a reduction in syneresis of said treated mass relative to an untreated mass; (ii) an increase in viscosity of said treated mass relative to an untreated mass; and (iii) a lack of pectin depolymerisation. Tomato juice, tomato slurry, tomato paste, salsa and ketchup are mentioned as examples of pectin-containing foods. Example 1 describes the preparation of a ketchup products from a diluted hot break tomato paste (8.5% VSS) that has been homogenised at 300 bar. The homogenized material was treated with different amounts of pectin esterase, followed by addition of brine, sugar, salt and acetic acid. The ketchup products so obtained were heated to 88° C. for 3 minutes and subsequently cooled in an ice bath. The results indicate that syneresis and viscosity can be controlled by adjusting the concentration of pectin esterase.
U.S. Pat. No. 7,166,315 describes a composition comprising dietary fibres with high water holding capacity (WHC) that is obtained from tomato pulp. The composition can be used as a texturing, bulking, viscosity controlling or syneresis-preventing agent for food. The US patent further describes a process for preparing the aforementioned composition comprising:    1) pre-treating tomatoes by conventional unit operations which comprise washing, sorting and crushing,    2) separating the peel and seeds of the tomato from the crushed tomatoes,    3) subjecting the crushed tomatoes to heat treatment (80-110° C.),    4) separating the crushed tomatoes into serum and pulp by centrifugation, to obtain fine pulp,    5) extracting carotenoids and lipids from the fine pulp obtained in step 4, and    6) drying the extracted fine pulp obtained in step 5;and wherein the peels and seeds of the tomato are separated from the crushed tomatoes at any stage before said extracting and drying. Following the separation stage, carotenoids and lipids are extracted from the fine pulp to obtain, after solvent removal, tomato fibres substantially free of lipids, carotenoids, seeds and peels The solvent may then be removed by azeotropic distillation.
From a consumer perspective both the use of enzymes and organic solvents as advocated in the above referenced US patents are equally undesirable as the use of additives described herein before. Hence, there is a need for alternative techniques that enable the industrial production of high quality tomato-based products, but that do not employ additives, enzymes or organic solvents. More particularly, there is a need for a “friendly label” agent that can be applied in tomato-based products to increase viscosity and/or to prevent syneresis.